The invention relates to improvements in surgically implantable cardiac pacemakers. More particularly, the invention relates to improvements in pacemakers of the type having a subcutaneously implantable pulse generator and one or more pulse transmitting leads extending from the pulse generator to the heart of the patient.
Cardiac pacemakers of the type to which the present invention pertains are disclosed, for example, in U.S. Pat. No. 3,198,195 to Chardack. Surgically implantable pulse transmitting leads are disclosed in U.S. Pat. No. 4,393,883 to Smyth et al. A drawback of the patented pacemakers and of other presently known implantable pacemakers is that any, even minor, failure of the pulse generator and/or of the leads necessitates complex and often painful and expensive surgery. The implanted parts of a cardiac pacemaker are bound, or at least likely, to fail and each such failure necessitates a lengthy and careful examination of the patient in order to ascertain the cause and/or extent of the failure. For example, the energy source or sources of the pulse generator are likely to be exhausted earlier than anticipated, the electric circuitry of the pulse generator can develop a short or another defect, or the tips of the electrodes which are implanted in the heart of the patient become dislodged with attendant intensification or weakening of the transmitted pulses. The implanted pacemaker is further likely to develop sensing problems which can involve a failure to properly synchronize the cardiac pulses with those which are transmitted by the pulse generator.
The situation is aggravated if the implanted pacemaker develops defects which are of intermittent nature and/or which do not induce the patient to develop clear-cut reactions. In accordance with heretofore known techniques, intermittent or non readily detectable failures of the implanted pacemaker necessitate complete removal of the pulse generator and/or pulse transmitting lead or leads from the patient's body with attendant risks and problems which are invariably involved in carrying out such delicate surgery.